1. Field of the Invention
The present invention relates to a magnetoresistive effect element and a magnetic memory.
2. Related Art
Magnetoresistive effect elements using magnetic material films are used in, for example, magnetic heads and magnetic sensors. In addition, it is proposed to use the magnetoresistive effect elements in solid state MRAMs (Magnetic Random Access Memories).
As a magnetoresistive effect element which has a sandwich structure film formed by inserting a single layer of a dielectric between two ferromagnetic layers, which causes a current to flow perpendicularly to the surface, and utilizes a tunnel current, the so-called “ferromagnetic TMR (Tunneling Magneto-Resistance effect) element” is proposed in recent years. Since it has become possible to obtain a magnetoresistance change rate of 20% or more in the TMR element, technical development for public welfare application of the element to the MRAM is being conducted vigorously.
This TMR element can be implemented by forming a thin Al (aluminum) layer having a thickness in the range of 0.6 to 2.0 nm on a ferromagnetic layer, exposing a surface of the Al layer to oxygen glow discharge or oxygen gas, and thereby forming a tunnel barrier layer formed of Al2O3.
A ferromagnetic single tunnel junction having a structure obtained by providing one of the ferromagnetic layers having the tunnel barrier layer of a ferromagnetic single tunnel junction between with an antiferromagnetic layer is proposed. Furthermore, a ferromagnetic tunnel junction having magnetic particles scattered in a dielectric, and a ferromagnetic double tunnel junction having a continuous film as each of the ferromagnetic layers.
These magnetoresistive effect elements also have a possibility of being applied to the MRAMs because it has become possible to obtain a magnetoresistance change rate in the range of 20 to 50% and the decrease of the magnetoresistance change rate can also be suppressed by raising the voltage value applied to the TMR element to obtain a desired output voltage value.
The magnetic recording element using the ferromagnetic single tunnel junction or the ferromagnetic double tunnel junction is non-volatile, and has a potential that a write and read time is 10 nanoseconds or less and the number of times of rewriting is also 1015 or more. Especially in the magnetic recording element using the ferromagnetic double tunnel junction, the decrease of the magnetoresistance change rate can be suppressed even if the voltage value applied to the ferromagnetic tunnel junction element is raised, as described above. Therefore, a large output voltage is obtained, and characteristics that are favorable as the magnetic recording element are obtained.
Since inversion is conducted using a current magnetic field based on a current pulse when writing to the magnetic recording layer is executed, power consumption is high. When the capacity is increased, there is a limit in allowable current density for wiring and consequently a large capacity cannot be obtained. Unless the absolute value of the current is 1 mA or less, or it is 0.2 mA or less for substitution for DRAMs, the area of the driver for letting flow a current increases. As compared with other non-volatile solid-state magnetic memories, such as ferro-electric random access memories using ferroelectric capacitors or flash memories, there is a problem that the chip size becomes large and competitive power is lost.
In order to solve the above-described problem, a solid-state magnetic storage device having a thin film formed of a high permeability magnetic material around writing wiring is proposed. According to these magnetic memories, a high permeability magnetic film is provided around wiring, and consequently a current value required to write information into the magnetic recording layer can be reduced efficiently.
Even if high permeability magnetic films are used, however, it is very difficult to cause the write current value to become 1 mA or less.
In order to solve these problems, a write method using a spin injection method is proposed (see, for example, U.S. Pat. No. 6,256,223). This spin injection method utilizes inversion of the magnetization direction of the magnetic recording layer obtained by injecting a spin-polarized current into the magnetic recording layer of the memory element.
In the case where the spin injection method is applied to the TMR element, there is a problem of element destruction such as breakdown of a tunnel insulation film and there is a problem in element reliability.
Therefore, it is necessary to provide a material, structure and architecture of a new magnetoresistive effect element and a spin memory which are small in current density at the time of writing to the extent that element destruction is not caused even if writing is conducted using the spin injection method, which have resistance to heat fluctuation, and which are small in interaction with adjacent cells.
As described heretofore, a material, structure and architecture of a new magnetoresistive effect element and a spin memory which operate with low power consumption and low current writing, which are highly reliable without element destruction, which have resistance to heat fluctuation, and which are small in interaction with adjacent cells are needed.